1. Field of the Invention
The present invention relates to an optical displacement detection apparatus and an optical displacement detection method, which adaptively adjust the light spectrum according to reflected light from a detected object, so as to determine the displacement more accurately.
2. Descriptions of the Related Art
Optical displacement detection apparatus has been widely used in many applications, one of which is the optical mouse. In an optical mouse, light emitted from a light source is projected on the surface of a desk or an object, reflected thereby, and received by a sensor chip which is disposed in the optical mouse. The sensor chip converts the optical signals into electronic signals, which are processed by a processor to determine the displacement of the mouse.
Currently, there are two types of mice, one of which employs a general light emission diode (LED), most often red LED, to emit light, and the other of which employs a laser diode (LD) to emit laser beams. In the context of this specification, a mouse which employs the LED is referred to as a “general optical mouse,” while a mouse which employs the LD is referred to as a “laser mouse”, and collectively named as “optical mice.”
The general optical mouse and the laser mouse operate under the same principle. The differences are in the light spectrums and the capability to recognize the surface under detection. A general optical mouse detects the pattern on the surface, and a laser mouse detects the roughness of the surface. Hence, each type of mouse has its advantages and weaknesses.
More specifically, for a general optical mouse, when the surface under detection has a color similar to the color of light emitted by the LED, the light scattering effect will seriously reduce the sensitivity of the sensor chip to recognize the pattern on the surface. The features of the pattern become less recognizable, and lead to inaccurate displacement calculation.
As for a laser mouse, when the roughness of the surface under detection is low, even if there is a clear pattern on the surface, misjudgment may occur.
U.S. Pat. No. 6,963,059 proposes a method to regulate the power of a light source. However, this does not solve the above problems.
Furthermore, it is understandable that the entire energy of the light beam is constant and the sensitivity of an optical mouse would depend on the optical strength or the illumination area of the light beam. When the illumination area of the light beam is smaller, the optical strength would be greater; on the contrary, when the illumination area of the light beam is wider, the optical strength would be weaker. It would be more significant when the optical mouse is working in a poor light-reflecting or scattering environment. The light strength received by the sensor would be much weaker and thus erroneous detections may probably occur.
Furthermore, in the laser mouse, a laser diode is adopted as the light source. The laser beams are always regulated at a certain angle according to a certain environment or working surface. However, the sensitivity of the laser optical mouse would be influenced due to different reflection indexes of the different operational surfaces. For example, when a laser optical mouse designed for a rough surface is working on a flat surface, merely very few of the reflected light beams would be detected by the sensor and thus the sensitivity would be decreased. If plural sets of lens are equipped for different surfaces to solve the problems, it would bring other disadvantages such as increasing the manufacturing cost and the volume of the optical mouse.
As for the sensor, it is generally constituted by a plurality of sensor unites to determine the movement by sensing the speckles from the reflective surface. Conventionally, a distance between the geometric centers of any two sensor units of the sensor chip is larger than 30 micrometers. However, the conventional laser optical mouse may be insufficient to accurately determine the movement because a distance between any two speckles formed by the laser diode illuminating surface details on the laser optical mouse is only about 7 micrometers, which is much shorter than 30 micrometers.